The setting: A favorite of early environmentalist John Muir, Yosemite combines sheer rock cliffs and Sequoia forests that rise up the western slopes of the Sierra Nevada range.

The inside scoop: Come summer, "Yosemite Valley is full and can feel overwhelming," says Lissie Kretch, who spent four years working for the Yosemite Institute, which runs environmental education programs. "But getting out of your car and onto a trail means you lose most of the visitors." One of the valley's less-visited routes runs from Mirror Lake to Snow Creek Falls, an eight-mile round-trip with gorgeous views of Half Dome.

Plan B:Tuolumne Meadows (pictured) opens only in the summer, so the human impact is reduced. Kretch recommends "finding a spot to sit and watch the clouds burst along the Tuolumne River. If you're up for it, hike Mount Hoffman, which is the geographical center of the park and supposedly Muir's favorite peak."